1. Field of the Invention
The present invention relates to a method of correcting a measurement error, in which the impedance of an electronic component measured by an actual measuring device is corrected to the impedance which will be obtained when measurement is performed by using a standard measuring device. Also, the present invention relates to a method of determining the quality of an electronic component using the correction method, and a device for measuring the characteristic of an electronic component for performing the correction method.
2. Description of the Related Art
The impedance of an electronic component or the same type of electronic components may be measured by a plurality of measuring devices, for example, a measuring device of the manufacturer of the electronic component and that of a user.
In this case, a different measurement error occurs depending on the used measuring device. Therefore, the reproducibility of the measurement value is low, that is, when an electronic component is measured by different measuring devices, the measurement results are not the same.
When impedance in a low-frequency band is measured, the measurement error is relatively insignificant, which leads to only a small problem. However, when impedance in a high-frequency band of 1 MHz to 2 GHz is measured, the difference between measurement errors generated by different measuring devices is significant. Therefore, in order to enhance the reproducibility of a measurement value in a high-frequency band, a measured value is corrected by using an open/short correction method or an open/short/load correction method. Hereinafter, these correction methods will be described. Incidentally, measurement of impedance which is performed in the following known art and in an embodiment described later conceptually includes measurement of admittance.
In the open/short correction method, impedances of two states: a test fixture (hereinafter referred to as jig) is open/short, are measured in order to correct the effects of stray admittance and residual impedance generated by the jig. Then, the characteristic (impedance) of an object is calculated based on the obtained impedance values.
In the open/short/load correction method, the above-described open/short measurement is performed first. Then, in a state where a load device, whose physical true value is known, is loaded on the jig, the above-described open/short measurement is performed. After that, the characteristic (impedance) of an object is calculated based on the obtained impedance values. In this method, correction can be performed more precisely than in the open/short correction method (see HP 4284A Precision LCR meter instruction manual (December 1996/33) p.6-15 to p.6-18, for example).
In the above-described known open/short correction method, one of the following two conditions must be satisfied.
First condition: impedance should be measured in an ideal open state or an ideal short state in order to obtain the effects of stray admittance and residual impedance.
Second condition: the values of impedance of the jig in open/short states are known.
However, these conditions cannot be satisfied for the following reason. That is, the ideal open/short states of the jig cannot be realized practically, and thus the first condition cannot be satisfied.
Also, stray admittance is generated when the jig is in an open state, and residual impedance is generated when the jig is in a short state. Therefore, in the above-described known art, the following instructions are given:
An operator should not move his/her hands near the jig while an open correction is performed in order to suppress variation in stray admittance.
A metallic plate having a high conductivity should be used for a short plate included in a short device used for short correction in order to suppress residual impedance to as low as possible.
However, even if these instructions are faithfully followed, it is impossible to realize true open/short states, and thus correction cannot be performed with great precision.
Of course, the open/short/load correction method has the same disadvantage as that of the open/short correction method. Furthermore, in the open/short/load correction method, a calibration value of the device used for load correction cannot be measured precisely. This will be described below.
In the open/short/load correction method, a device whose physical true value is known (hereinafter referred to as standard device) is required in order to perform load correction. According to the above-described known art, an electronic component (chip capacitor, chip coil, etc.) whose impedance is measured in advance can be used as a standard device. However, this correction method can be used only when a measured frequency is sufficiently low and measurement precision can be maintained even if the effects of stray admittance and residual impedance are ignored. Specifically, this correction method can be used when the measured frequency is 1 MHz or less.
In recent years, however, with a requirement for higher frequency of signal band, a guarantee of impedance in a high-frequency band of 1 MHz to several GHz has been required to electronic components. However, in the above-described correction methods, a correction precision required for such a guarantee of impedance in a high-frequency band cannot be obtained.
When impedance is measured in a high-frequency band of 1 MHz to several GHz, the effects of stray admittance and residual impedance cannot be ignored. Therefore, precise stray admittance and residual impedance must be obtained in order to realize sufficiently high correction precision. In order to obtain precise stray and residual characteristics, the impedance of an electronic component which is used as a standard device must be measured with great precision.
However, in order to precisely measure the impedance of the electronic component, a jig used for measuring the electronic component must be corrected, and in order to perform the correction, another standard device is required. Accordingly, it is practically impossible to realize a high-precision correction in a high-frequency band of 1 MHz to several GHz by using the open/short/load correction method, as long as an extremely precise standard device cannot be obtained.
If an object to be measured includes a coaxial connector, a standard device in which the physical true value of impedance is very precisely defined can be available. However, such a standard device can be fabricated only in an electronic component having a shape which can be attached to a coaxial connector. It is practically impossible to fabricate such a standard device in general electronic components, such as chip capacitors and chip coils.